The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

The second edition of The Biomarker Guide is a fully updated and expanded version of this essential reference. Now in two volumes, it provides a comprehensive account of the role that biomarker technology plays both in petroleum exploration and in understanding Earth history and processes. Biomarkers and Isotopes in the Environment and Human History details the origins of biomarkers and introduces basic chemical principles relevant to their study. It discusses analytical techniques, and applications of biomarkers to environmental and archaeological problems. The Biomarker Guide is an invaluable resource for geologists, petroleum geochemists, biogeochemists, environmental scientists and archaeologists.

The Biomarker Guide

Understanding the origin of the carbon (C) stabilised in soils is crucial in order to device management practices that will foster Caccumulation in soils. The relative contributions to soilC pools of roots vs. shoots is one aspect that has been mostly overlooked, although it appears a key factor that drives the fate of plant tissueC either as mineralized CO2 or as stabilized soil organic matter (SOM). Available studies on the subject consistently indicate that rootC has a longer residence time in soil than shootC. From the few studies with complete datasets, we estimated that the mean residence time in soils of root-derived C is 2.4times that of shoot-derived C. Our analyses indicate that this value is biased neither by an underestimation of root contributions, as exudation was considered in the analysis, nor by a priming effect of shoot litter on SOM. Here, we discuss the main SOM stabilisation mechanisms with respect to their ability to specifically protect root-derived SOM. Comparing in situ and incubation experiments suggests that the higher chemical recalcitrance of root tissues as compared to that of shoots is responsible for only a small portion, i.e. about one fourth, of the difference in mean residence time in soils of root-derived vs. shoot-derivedC. This suggests that SOM protection mechanisms other than chemical recalcitrance are also enhanced by root activities: (1)physico-chemical protection, especially in deeper horizons, (2)micrometer-scale physical protection through myccorhiza and root-hair activities, and (3)chemical interactions with metal ions. The impact of environmental conditions within deeper soil layers on rootC stabilisation appear difficult to assess, but is likely, if anything, to further increase the ratio between the mean residence time of root vs. shootC in soils. Future advances are expected from isotopic studies conducted at the molecular level, which will help unravel the fate of individual shoot and root compounds, such as cutins and suberins, throughout soil profiles.

Is soil carbon mostly root carbon? Mechanisms for a specific stabilisation

Mechanisms to mitigate global climate change by sequestering carbon (C) in different ‘sinks' have been proposed as at least temporary measures. Of the major global C pools, terrestrial ecosystems hold the potential to capture and store substantially increased volumes of C in soil organic matter (SOM) through changes in management that are also of benefit to the multitude of ecosystem services that soils provide. This potential can only be realized by determining the amount of SOM stored in soils now, with subsequent quantification of how this is affected by management strategies intended to increase SOM concentrations, and used in soil C models for the prediction of the roles of soils in future climate change. An apparently obvious method to increase C stocks in soils is to augment the soil C pools with the longest mean residence times (MRT). Computer simulation models of soil C dynamics, e.g. RothC and Century, partition these refractory constituents into slow and passive pools with MRTs of centuries to millennia. This partitioning is assumed to reflect: (i) the average biomolecular properties of SOM in the pools with reference to their source in plant litter, (ii) the accessibility of the SOM to decomposer organisms or catalytic enzymes, or (iii) constraints imposed on decomposition by environmental conditions, including soil moisture and temperature. However, contemporary analytical approaches suggest that the chemical composition of these pools is not necessarily predictable because, despite considerable progress with understanding decomposition processes and the role of decomposer organisms, along with refinements in simulation models, little progress has been made in reconciling biochemical properties with the kinetically defined pools. In this review, we will explore how advances in quantitative analytical techniques have redefined the new understanding of SOM dynamics and how this is affecting the development and application of new modelling approaches to soil C.

Soil organic matter turnover is governed by accessibility not recalcitrance

Background/Context: Educators have written about and studied school climate for 100 years. School climate refers to the quality and character of school life. School climate is based on patterns of people’s experiences of school life and reflects norms, goals, values, interpersonal relationships, teaching and learning practices, and organizational structures. However, school climate is more than individual experience: It is a group phenomenon that is larger than any one person’s experience. A sustainable, positive school climate fosters youth development and learning necessary for a productive, contributive, and satisfying life in a democratic society. This climate includes norms, values, and expectations that support

School Climate: Research, Policy, Practice, and Teacher Education

http://www.chm.bris.ac.uk/~chidb/personal/content/paper10.pdf

Organic geochemical studies of soils from the Rothamsted classical experiments : V. The fate of lipids in different long-term experiments

A review of our current understanding of resistant biomacromolecules derived from present and past algae and higher plants is presented. Insight in the nature of recent and fossil macromolecules is strongly hampered by the difficulties in obtaining the material in pure and unaltered form. For the extant material, avoiding artificial condensation and structural alteration as a result of chemical isolation and purification of biomacromolecules requires constant attention. To date, several types of sporopollenin seem to occur. One type is characterised by oxygenated aromatic building blocks, in particular p-coumaric acid and ferrulic acid. The other type is thought to consist predominantly of an aliphatic biopolymer. In this review it is concluded that extant sporopollenin consists of the aromatic type, whereas the aliphatic component of fossil sporopollenin is due to early-diagenetic oxidative polymerization of unsaturated lipids. The cuticles of most higher plants contain the aliphatic biopolyester cutin. Additionally, cuticles of drought-adapted, mostly CAM plants, seem to contain the non-hydrolysable aliphatic biopolymer cutan. Only a very few algae are able to biosynthesize resistant, (fossilisable) cell walls: some Chlorophyta, Eustigmatophyta and Prasinophyta produce the aliphatic biopolymer algaenan. Some Dinophyta are also capable of producing algaenan cell walls. Additionally, some taxa produce highly resistant cyst-walls with a high proportion of aromatic moieties. For the morphologically well-preserved fossil material, contamination by organic particles other than the target taxon is hard to eliminate and can contribute to either the aliphatic or aromatic signal. Furthermore, post-mortem migration of aliphatic moieties into, and their condensation onto the macromolecule might occur, e.g. by oxidative polymerization. These phenomena hamper the evaluation of the aliphatic signature of fossil plant material and may for example explain the preservation of initially cutin-based cuticles or non-algaenan containing algae. The extent to which migration and in situ formation of aromatic moieties plays a role in modifying resistant algal macromolecules, notably under elevated temperature and/or pressure conditions, still remains an open question.

/pdf/biomacromolecules-of-algae-and-plants-and-their-fossil-2t3gg3cuui.pdf

Biomacromolecules of Algae and Plants and their Fossil Analogues

Studies performed during the last two decades have shown that lipids are preserved in association with a wide range of artefacts and ecofacts recovered from archaeological sites, e.g. pottery vessels and skeletal remains. The majority of work in this area has focused on the use of molecular structures ('biomarkers') and distributions ('fingerprints') to assess the nature and origin of commodities associated with past cultural, economic and agricultural practices. However, since lipids, like all other classes of biomolecule, are affected by degradation (both pre- and post-burial), emphasis is now being placed on the complementary use of diagenetically robust, compound-specific stable isotope measurements to enhance the scope and reliability of archaeological interpretations. A feature of the δ13C values of individual lipids, rather than bulk measurements of biochemically more heterogeneous materials, lies in their capacity to reflect differences in both the isotopic composition of the carbon sources used in their biosynthesis and the routing of dietary lipids and their metabolites in consumer organisms. This isotopic information, accessible by gas chromatography-combustion-isotope ratio mass spectrometry, has opened up new avenues of investigation concerning human activity in prehistory.

Lipids as carriers of anthropogenic signals from prehistory

While oxidation products of unsaturated fatty acids, for example dicarboxylic acids (hereafter diacids), must form during the use of unglazed ceramic vessels for the processing of animal and plant products, such components have never been observed during studies of absorbed lipids. Their absence from the extractable lipid fraction is presumed to be the result of their loss from potsherds through groundwater leaching. Lipid oxidation products including short-chain dicarboxylic acids, ω-hydroxy acids and longer-chain hydroxy and dihydroxy acids have now been observed as components probably covalently bound into solvent insoluble residues of potsherds recovered from waterlogged deposits. These components were only revealed following alkaline treatment of the insoluble residues. A similar mixture of diacids was observed in high abundance in the free lipid fraction of vessels recovered from an exceptionally arid deposit where groundwater leaching would never have occurred. These results confirm the formation of oxidation and probable polymerization products of unsaturated fatty acids during vessel use and burial.

/pdf/free-and-bound-fatty-acid-oxidation-products-in-7orzshgepm.pdf

Free and bound fatty acid oxidation products in archaeological ceramic vessels

Organic geochemical studies of soils from the Rothamsted Classical Experiments—II, Soils from the Hoosfield Spring Barley Experiment treated with different quantities of manure

Pim F. van Bergen

Papers

Organic geochemical studies of soils from the Rothamsted classical experiments : V. The fate of lipids in different long-term experiments

Biomacromolecules of Algae and Plants and their Fossil Analogues

Lipids as carriers of anthropogenic signals from prehistory

Free and bound fatty acid oxidation products in archaeological ceramic vessels

Organic geochemical studies of soils from the Rothamsted Classical Experiments—II, Soils from the Hoosfield Spring Barley Experiment treated with different quantities of manure